1. Field of the Invention
This invention relates generally to antenna sensors and more particularly to a millimeter wave, infrared and laser sensor employing a common receiving aperture.
2. Description of Related Art
Single mode sensors used, for example, in missile seekers are known to exhibit degraded performance because of false target acquisitions. In order to overcome this inherent deficiency, a dual-mode seeker including millimeter wave (MMW) and infrared (IR) sensors has been developed. One such system which substantially improves false alarm rate is shown and described in U.S. Pat. No. 5,214,435 entitled, xe2x80x9cMillimeter Wave and Infrared Sensor In A Common Receiving Aperturexe2x80x9d, issued to T. C. Brusgard et al. on May 25, 1993, the details of which are incorporated herein by reference. There an integrated millimeter wave (MMW) and an infrared (IR) common aperture sensor includes a common primary reflector for infrared and millimeter wave energy. An active transmitter/receiver millimeter wave horn assembly located at the focus of the primary mirror transmits and receives millimeter wave signals off of the primary reflector. A selectively coated dichroic element is located in the path of the millimeter wave energy on the axis between the feed and the primary reflector. The dichroic element reflects infrared energy from the primary mirror to a focal point and at the same time transmits and focuses millimeter wave energy to a transmitter/receiver. An optical system relays the infrared energy to a focal plane behind the primary mirror. The dichroic element transmits and focuses millimeter wave energy without significant attenuation such that optical and millimeter wave energy may be employed on a common boresight. Weather conditions and the time of day may adversely affect the ability of an infrared sensor to acquire the target while not affecting millimeter wave energy. Infrared has better resolution at closer ranges and the two can complement each other in target acquisition and rejection of countermeasures.
Although a single mode laser type missile seeker is also known, it relies on an external laser designator to pick out a target which further ensures reliable target acquisition. However, the laser designation may not be on the sweetest part of the target and the infrared can determine the optimum terminal aimpoint. Weather also affects the range performance of a laser designator system.
As processing has gotten faster and sensors have gotten smaller, more capability can be put into the same volume. This is particularly true of missile seekers and their capability to autonomously find and negate targets.
It is an object of the present invention, therefore, to provide an improvement in multi-mode sensors.
It is another object of the present invention to provide an assembly of multi-mode sensors located in a common receiving aperture.
It is still another object of the invention to provide a seeker having multi-mode sensors located in a common receiving aperture so as to minimize platform size and weight while providing essentially no increase in volume.
These and other objects are achieved by an improvement in the system taught in the above referenced Brusgand et al. patent by the inclusion of a laser spot tracker in the system. In the present invention, a single receiving aperture collects energy from a millimeter wave (MMW) RF sensor, an infrared (IR) sensor and a semi-active laser energy sensor aligned on a common central axis. An active millimeter wave transmitter/receiver is located at the focus of a primary mirror aperture. A selectively coated dichroic element is located in the path of millimeter wave energy and feeds the energy to an RF detector while reflecting infrared energy from the primary reflector to an optics system which re-images the IR energy on an infrared detector. The edge of the primary mirror is furthermore bent so that laser energy focuses beyond the RF receiver and thus produces no detrimental affects on either the RF or the IR energy received. The laser energy is captured using a second lens system located in front of the dichroic element and the RF receiver.
Since weather affects the performance of both IR and laser type sensor/receivers, an RF sensor can locate a target until the laser and infrared receiver can get close enough to see through any adverse weather.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific examples, while disclosing the preferred embodiments of the invention, it is given by way of illustration only, since various changes and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.